Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$155.49	6.405%	$165.4491	$165.45	$165.45	$165.40
Purchase #2	$59.58	12.706%	$67.1502	$67.15	$67.15	$67.20
Purchase #3	$35.69	10.702%	$39.5095	$39.51	$39.50	$39.50
Purchase #4	$117.97	12.340%	$132.5275	$132.53	$132.55	$132.50
Purchase #5	$26.29	12.432%	$29.5584	$29.56	$29.55	$29.60
Purchase #6	$12.93	4.307%	$13.4869	$13.49	$13.50	$13.50
Purchase #7	$113.82	10.730%	$126.0329	$126.03	$126.05	$126.00
7 purchase totals =	$521.77		$573.7145	$573.72	$573.75	$573.70